In the current state of the prior art, techniques utilized to correct vibrations generated in vehicular tires are basically modifications of balancing devices utilized in industry to balance industrial components, such as rotors. The state of the art is such that industry can achieve accurate balance and freedom from vibration in any type of rotor. Balancing can be readily accomplished since a rotor is effectively a homogeneous non-flexible mass, and it is always supported in bearings while freely rotating in space, whether during balancing or in actual use. A rotor, once balanced, has its principal axis of rotation rotating in coincidence with its bearing axis.
A rubber tire, unlike a rotor, is not a solid mass; rather, a tire is flexible and expands and contracts in use and is not geometrically round. The radius of a load supporting tire in the area of contact with the road is always smaller than its radius at any other angle about the tire. As the tire revolves the physical geometrical center of teh tire is never coincident with its principal bearing axis, as encountered in any other type of rotor, including a tire freely rotating in space.
While it has hitherto been proposed to hone the outside pheriphery of rubber tires to improve their concentricity, in many instances the vibratory effects of the tire are worsened rather than improved. It is significant to note that the force measurements utilized by the prior art to determine where on the tire the honing should take place were not made while the tire was rotating under true environmental-like condition; that is, the measurements were taken while the tire was being revolved at speeds of approximately 1 to 5 m.p.h. Consequently, such measurements do not take into account the effects of the non-uniform amplified centrifugal forces encountered when the tire is rotated at actual highway speeds, that is, at speeds in excess of 35-40 m.p.h. under which conditions the tire expands radially outwardly in an irregular manner producing hump-like irregularities. These irregularities vary in length, height and location about the periphery of the tire and are intensified by the fact that as the tire expands its elasticity is also affected, the tire reacting as if it were inflated with much greater air pressure.
While prior to the work of the present inventor, there was a recognition by the prior art of the existence of force variations which are centrifugally generated at high speeds, as well as a recognition that honing the tire at slow speeds does not correct for such centrifugally generated forces, there was no known way to accurately measure the forces involved much less make the necessary corrections even if the magnitude and location of the forces were known. The state of the art was such that it was literally impossible to segregate and measure these centrifugally generated forces, and it was equally impossible to correct the tire while rotating it at high speeds.
The present inventor, in his copending U.S. Pat. No. 3,862,570, dated Jan. 28, 1975, has taught a measuring system by means of which the forces generated in a tire under load and at high speeds can be accurately measured as well as segregated. In accordance with the teachings of this patent, both the dynamic unsymmetrical forces and the centrifugally generated forces which are the result of radially loaded peripheral non-uniformities are simultaneously measured and recorded by means of a closed loop piezoelectric measuring system so that appropriate corrective measures may be taken. Two sets of sensors are utilized, the first set measuring lack of symmetry (unbalance) on both sides of the tire, and the second set measuring centrifugally generated non-uniformities as they appear in the area of the tire patch, which is the area in contact with the road, and hence of vital importance.
An integrated system for correcting a tire both for peripheral non-uniformities and for lack of symmetry is taught in the present inventor's co-pending application Ser. No. 623,639, filed Oct. 20, 1975. In accordance with the teachings of this application, the measuring system of the aforementioned patent is utilized to measure both the magnitude and location of the forces generated by peripheral non-uniformities and also the magnitude and location of the forces generated by lack of tire symmetry. The measuring means generate signals which are fed to a digital computer which governs the correction of the tire in a two-stage corrective procedure, the first stage comprising the honing of the outside periphery of the tire while it is being revolved at cruising speed at the proper locations and in sufficient amounts to effectively remove the non-uniform areas which are developed in the tire. Concurrently the measuring means also determines and feeds to the computer signals indicating the locations and amounts of weight necessary to counterbalance the forces generated by lack of symmetry in the tire once it has been corrected for the peripheral non-uniformities.
The present invention relates to the corrective system of the aforementioned co-pending application, with particular reference to that portion of the system on which the tire is measured and honed to correct for peripheral non-uniformities, although as will become apparent, the present invention also incorporates techniques for marking the tire to facilitate subsequent correction for lack of symmetry. In order to place the present invention in proper perspective, it must be understood that the conventional automobile moving at a speed of 60 m.p.h. travels 88 feet per second, which is equivalent to 1056 inches per second. Stated in another way, a 1 inch length of the tire periphery enters the tire patch in less than 1 millisecond, that is, over 1000 Hz. Thus, at 60 m.p.h. a standard size automobile tire revolves approximately 12 times per second and during each revolution covers approximately 88 inches of road surface. In other words, a 1 inch length of the periphery of the tire becomes tangentially in contact with the road and begins to support the weight load of the vehicle in less than 0.001 second. Relating this data to a measuring and correcting system for honing the periphery of the tire, the honer must be actuated to contact the leading edge of an irregular growth area on the tire in 1 millisecond and retract fully away from the tire in 1 millisecond at the trailing end of the non-uniform growth area, it being remembered that each 0.001 second represents 1 inch of tire peripheral surface. The present invention deals with a system capable of honing the tire within these parameters.